Genetically engineered mice have become the gold standard for animal models in cancer. They are widely used to mimic human cancers with specific point mutations in tumor suppressor genes, as well as tissuespecific expression of mutations in somatic tissues. By combining several mutations in one animal, it is now possible to phenocopy human cancers that were difficult to reproduce previously in animal models. The Genetically Engineered Mouse Facility (GEMF) provides valuable resources to Cancer Center members. It generates transgenic and gene-targeted mice, performs embryo rederivations to generate pathogen-free mice, and provides cryopreservation services to archive animal models. The Mouse Resource Facility (MRF), as part of the GEMF, provides vectors for construct development, northern blots of adult and embryonic tissues, genomic DNA and cDNA libraries, and BAG filter sets. The MRF also has a small colony of Cre and lacZ transgenic mice essential for generating conditional deletions in mice. The GEMF thus provides unique opportunities to faculty to develop sophisticated animal models to study a variety of cancer problems. The GEMF has been extremely successful in generating and maintaining mouse models. In the last five years, the GEMF has generated animal models for more than 300 projects for MDACC investigators and has cryopreserved more than 120 mouse lines. A >1000% increase has been achieved in utilization of mouse resources through the MRF. The lead facility coordinator has developed new, more efficient methods of generating embryos for use by the facility. She is responsible for training faculty and their staff, and provides genetic and technical expertise to many investigators in many different programs. In addition to the facility coordinator, the GEMF is staffed by 7 highly-trained technicians. In the past five years, the GEMF has served 96 different users who represent 19 of the 20 sponsored programs; 97% of the investigators served are MDACC faculty. To better serve the needs of our investigators and add needed capacity, a small satellite facility was added recently to the South Campus. This expansion will enable the GEMF to develop more models and offer additional services. The GEMF is currently funded from multiple sources, including 53% provided by the CCSG and 45% recovered through user fees, with the remainder provided by MDACC.